Methods and systems for discriminating between ventricular waveforms when ventricular rate exceeds atrial rate

Abstract

A ventricular rate based on first candidate waveforms and second candidate waveforms within sensed ventricular waveforms is compared to an atrial rate. If the ventricular rate exceeds the atrial rate, the first candidate waveforms and second candidate waveforms are compared to a ventricular polarization complex template to obtain a first morphology indicator and a second morphology indicator. If a morphology match inconsistency is present, the amount by which the ventricular rate exceeds the atrial rate is compared to a threshold. If the threshold is exceeded, high-ventricular-rate therapy to the heart is inhibited. The ventricular polarization complex template may be a QRS-complex template, in which case a match inconsistency is present if each of the first candidate waveforms and the second candidate waveforms do not match the QRS-complex template. Alternatively, the ventricular polarization complex template may be a T-wave template, in which case a match inconsistency is present if either of the first candidate waveforms and the second candidate waveforms matches the T-wave template.

1. A method for discriminating between cardiac signal waveforms using an implantable medical device, said method comprising:
 sensing atrial waveforms of a heart and determining an atrial rate based on the atrial waveforms; 
 sensing ventricular waveforms of the heart and determining a ventricular rate based on first candidate waveforms and second candidate waveforms within the ventricular waveforms; 
 determining if the ventricular rate exceeds the atrial rate; 
 if the ventricular rate exceeds the atrial rate, comparing each of the first candidate waveforms of the ventricular waveforms and the second candidate waveforms of the ventricular waveforms to a first predetermined waveform template to obtain a first morphology indicator and a second morphology indicator, wherein the first and second morphology indicators represent a degree to which the respective first and second candidate waveforms match the first predetermined waveform template; 
 determining if the ventricular rate is correct, based on one or both of the first morphology indicator and the second morphology indicator; 
 if the ventricular rate is correct, applying therapy; 
 if the ventricular rate is incorrect, comparing the ventricular rate to the atrial rate to determine if the ventricular rate exceeds the atrial rate by a threshold amount; and 
 if the ventricular rate exceeds the atrial rate by the threshold amount, inhibiting the application of therapy to the heart, otherwise applying therapy. 
 
     
     
       2. The method of  claim 1 , wherein the first predetermined waveform template is representative of a QRS complex, and the ventricular rate is determined to be correct when the first morphology indicator indicates that the first candidate waveform matches the first predetermined waveform template and the second morphology indicator indicates that the second candidate waveform does not match the first predetermined waveform template. 
     
     
       3. The method of  claim 1 , wherein the first predetermined waveform template is representative of a T-wave, and the ventricular rate is determined to be incorrect when the first morphology indicator indicates that the first candidate waveform matches the first predetermined waveform template or the second morphology indicator indicates that the second candidate waveform matches the first predetermined waveform template. 
     
     
       4. The method of  claim 1 , wherein the comparing operation includes calculating a first area of the first candidate waveform with respect to a baseline, calculating a second area of the second candidate waveform with respect to the baseline and comparing each of the first and second areas to an area of the waveform template. 
     
     
       5. The method of  claim 1 , wherein the comparing operation comprises calculating an area of a fragment of the first candidate waveform with respect to a baseline, calculating an area of a fragment of the second candidate waveform with respect to the baseline, and comparing the areas of the fragment of each of the first and second candidate waveforms with an area of a fragment of the predetermined waveform template. 
     
     
       6. An implantable medical device for discriminating between cardiac signal waveforms, said device comprising:
 electrodes configured to be positioned proximate to a heart for sensing atrial waveforms of a heart and ventricular waveforms of the heart having first candidate waveforms and second candidate waveforms; and 
 a microcontroller configured to:
 determine an atrial rate based on the atrial waveforms, determine a ventricular rate based on the first candidate waveforms and the second candidate waveforms within the ventricular waveforms, and determine of the ventricular rate exceeds the atrial rate; 
 if the ventricular rate exceeds the atrial rate, compare each of the first candidate waveforms of the ventricular waveforms and the second candidate waveforms of the ventricular waveforms to a first predetermined waveform template to obtain a first morphology indicator and a second morphology indicator, wherein the first and second morphology indicators represent a degree to which the respective first and second candidate waveforms match the first predetermined waveform template; 
 determine if the ventricular rate is correct, based on one or both of the first morphology indicator and the second morphology indicator; 
 apply therapy if the ventricular rate is correct; 
 if the ventricular rate is incorrect, compare the ventricular rate to the atrial rate to determine if the ventricular rate exceeds the atrial rate by a threshold amount; and 
 if the ventricular rate exceeds the atrial rate by the threshold amount, inhibit the application of therapy to the heart, otherwise apply therapy. 
 
 
     
     
       7. The device of  claim 6 , further comprising an excitation source for applying therapy to the heart, wherein the first predetermined waveform template is representative of a QRS complex and the microcontroller determines the ventricular rate is incorrect when the first morphology indicator indicates that the first candidate waveform matches the first predetermined waveform template and the second morphology indicator indicates that the second candidate waveform does not match to the first predetermined waveform template. 
     
     
       8. The device of  claim 6 , further comprising an excitation source for applying therapy to the heart, wherein the first predetermined waveform template is representative of a T-wave and the microcontroller determines the ventricular rate is incorrect when the first morphology indicator indicates that the first candidate waveform matches the first predetermined waveform template or the second morphology indicator indicates that the second candidate waveform matches to the first predetermined waveform template.